include/c: use returns_nonnull function attribute in xalloc.h

Let the compiler optimize based on the knowledge that the return value will
never be null.

Reference: https://patchwork.ozlabs.org/patch/281112/#631159
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

2 files changed, 13 insertions, 5 deletions

diff --git a/include/c.h b/include/c.h
index b769b5843..8b2a2d19a 100644
--- a/include/c.h
+++ b/include/c.h
@@ -80,6 +80,12 @@
 # endif
 #endif
 
+#if (__GNUC__ >= 5) || ((__GNUC__ >= 4) && (__GNUC_MINOR__ >= 9))
+# define __ul_returns_nonnull __attribute__((returns_nonnull))
+#else
+# define __ul_returns_nonnull
+#endif
+
 /*
  * Force a compilation error if condition is true, but also produce a
  * result (of value 0 and type size_t), so the expression can be used
diff --git a/include/xalloc.h b/include/xalloc.h
index 8870ac0d9..1d225d4a0 100644
--- a/include/xalloc.h
+++ b/include/xalloc.h
@@ -26,7 +26,7 @@ static inline void __err_oom(const char *file, unsigned int line)
 
 #define err_oom()	__err_oom(__FILE__, __LINE__)
 
-static inline __ul_alloc_size(1)
+static inline __ul_alloc_size(1) __ul_returns_nonnull
 void *xmalloc(const size_t size)
 {
         void *ret = malloc(size);
@@ -36,7 +36,7 @@ void *xmalloc(const size_t size)
         return ret;
 }
 
-static inline __ul_alloc_size(2)
+static inline __ul_alloc_size(2) __ul_returns_nonnull
 void *xrealloc(void *ptr, const size_t size)
 {
         void *ret = realloc(ptr, size);
@@ -46,7 +46,7 @@ void *xrealloc(void *ptr, const size_t size)
         return ret;
 }
 
-static inline __ul_calloc_size(1, 2)
+static inline __ul_calloc_size(1, 2) __ul_returns_nonnull
 void *xcalloc(const size_t nelems, const size_t size)
 {
         void *ret = calloc(nelems, size);
@@ -56,7 +56,8 @@ void *xcalloc(const size_t nelems, const size_t size)
         return ret;
 }
 
-static inline char __attribute__((warn_unused_result)) *xstrdup(const char *str)
+static inline char __attribute__((warn_unused_result)) __ul_returns_nonnull
+*xstrdup(const char *str)
 {
         char *ret;
 
@@ -70,7 +71,8 @@ static inline char __attribute__((warn_unused_result)) *xstrdup(const char *str)
         return ret;
 }
 
-static inline char * __attribute__((warn_unused_result)) xstrndup(const char *str, size_t size)
+static inline char * __attribute__((warn_unused_result)) __ul_returns_nonnull
+xstrndup(const char *str, size_t size)
 {
         char *ret;